As the well-known compounds among the N-cyano-pyridinecarboximidamide compounds in relation to the present invention, there are mentioned N-cyano-3-pyridinecarboximidamide [see Journal of Medicinal Chemistry, 23, 690-692 (1980)], N-cyano-4-(2-ethylpyridine)carboximidamide (see Leprosy Review, 23-30, 1983) and N-cyano-4-pyridinecarboximidamide (see Bulletin des Societes Chimiques Belges, 78, 41-46, 1969). However, all of these compounds are the ones which have no substituent in N'-position and are reported only as the intermediates for producing of diuretics or as the agents for the treatment of Hansen's disease. There is no report of other utility. The syntheses of carboximidamides have been investigated from various aspects, and various synthetic methods mainly of benzenecarboximidamide compounds or alkylcarboximidamides are investigated (see, for example, "The Chemistry of amidines and imidates", Edited by Saul Patai, John Wiley and Sons, 1975). For example, in the case of an N-cyano-N'-substituted benzenecarboximidamide, a synthetic method which comprises converting cyanobenzene into an alkyl benzeneimidate, further reacting cyanamide (NH.sub.2 CN) with the alkyl benzeneimidate in pH 6.5-7.0 to form an alkyl N-cyano-benzeneimidate and reacting an amine compound with the aforementioned imidate has been proposed (see Synthesis, 263, 1971; Synthesis, 673-675, 1978; Journal of Organic Chemistry, 44, 1562-1563 (1979); Synthesis, 123-124, 1980; Synthesis, 402-404, 1983).
However, according to the conventional synthetic methods, particularly the synthesis within the above-described pH range, an alkyl N-cyano-pyridinecarboximidate is not produced, and thus an N-cyano-N'-substituted pyridinecarboximidamide compound could not be produced.
On the other hand, as regards antihypertensive agents, a variety of pharmaceutical agents have been proposed, but, so far as the present inventor knows, none of these agents have satisfactory effects on the pathologies and patients of all kinds of hypertensions such as essential hypertension, secondary hypertension or the like. Also as regards the treatment of angina pectoris, calcium antagonists or .beta.-blockers and the like have hitherto been used, but the attack of angina pectoris is not completely suppressed by the use of these agents. There are reported no therapeutics having satisfactory cardioprotective effect after the reperfusion of coronary vessel when the pathology develops into myocardial infarction. New types of cardiovascular therapeutics with consideration for these points are continuously desired.
For instance, as a cardiovascular therapeutic based on a new function mechanism, a compound having a potassium channel activating effect has recently been proposed.
The potassium channel activating effect is an effect that potassium channel on cell membrane is opened and the permeability of potassium is enhanced so that hyperpolarization is caused and the contraction of smooth muscle or myocardium is suppressed. As compounds having potassium channel activating effect, there are known, for example, nicorandil, pinacidil and chromakalim (see Trends in Pharmacological Sciences, 8, 283, 1987). These exhibit vasodilating effect, antihypertensive effect, coronary blood flow increasing effect, cerebral vasodilative effect and bronchodilatative effect in animal experiments [see European Journal of Pharmacology, 152, 331 (1988); The Journal of Pharmacology and Experimental Therapeutics, 232, 369 (1985); Journal of Cardiovascular Pharmacology, 8, 798 (1986); Japan Heart Journal, 20, 881 (1979); European Journal of Pharmacology, 99, 219 (1984); British Journal of Pharmacology, 95, 763 (1988)]. Furthermore, these agents clinically exhibit utilities as an antihypertensive drug [see Clinical Physiology, 1, 375 (1981); Journal of Hypertension, 4, S166 (1986)] or as an antianginal drug [see RINSHO YAKURI, 13, 311 (1982)].
As the well-known carboximidamide compounds except the N-cyano-pyridinecarboximidamide compounds relating to the present invention, there are mentioned N-cyano-5-nitro-2-furamidine (Japanese Patent Publication No. 20453/68 and British Patent No 1133950); N-cyano-2-thiophenecarboximidamide and N-cyano-3-thiophenecarboximidamide [Journal of Medicinal Chemistry, 23, 690-692 (1980)]; and N-(N-cyanoimidoyl)-sulfoximides [Chemisch Berichte, 121, 383-386 (1988)]. However, these compounds have been reported only as the intermediates in the production of anti-bacterial agents or diuretics and the intermediates in the production of thiatriazines, respectively, without descriptions of the vasodilating effect and hypotensive effect Also, no carboximidamide compounds relating to the present invention which have an alkyl substituent in N'-position have hitherto been reported.